Ethylene glycol is used extensively in the preparation of antifreeze compositions and may be prepared by various known processes. One such process, described in U.S. Pat. No. 1,982,545, involves the iodine catalyzed liquid phase oxidation of ethylene. Variations on this process are described, for example, in U.S. Pat. Nos. 3,928,474 and 4,045,500.
Generally, the said iodine catalyzed liquid phase reaction may be represented as follows: EQU CH.sub.2 .dbd.CH.sub.2 +I.sub.2 .fwdarw.ICH.sub.2 --CH.sub.2 I (1) EQU ICH.sub.2 --CH.sub.2 I+H.sub.2 O.fwdarw.HOCH.sub.2 --CH.sub.2 I+HI (2) EQU HOCH.sub.2 --CH.sub.2 I+H.sub.2 O.fwdarw.OHCH.sub.2 --CH.sub.2 OH+HI (3) EQU 2HI+1/2O.sub.2 .fwdarw.H.sub.2 +I.sub.2. (4)
The net reaction may be represented thus: EQU CH.sub.2 .dbd.CH.sub.2 +1/2O.sub.2 +H.sub.2 O.fwdarw.HOCH.sub.2 --CH.sub.2 OH.
The iodination of ethylene (1), the primary hydrolysis of ethylene iodide (2), and the oxidation of hydriodic acid (4) all proceed rapidly compared with the hydrolysis of ethylene iodohydrin (3). Since this latter reaction is the rate-limiting step of the process, it is desirable to devise means for accelerating the same. It has been found that improved yields of ethylene glycol are obtained when the said liquid phase reaction of ethylene, oxygen, and water is conducted in the presence of a mixed iodine/bromine catalyst, as compared with the same reaction catalyzed by iodine alone.